Unified tool head grip

I realize that it is difficult to foresee the needs of the masses, as modifications are ongoing. I also want to avoid boxing in or excluding those with wild ideas. But it seem a bit messy just to upgrade the extruder, or change to a laser, inkjet, mill or drill setup.

The grip could incorporate connectors for electrical power and data on specified locations and thus allow for kit-less remote designers to chip in with new or upgraded heads, following a universally accepted grip.

If the source is closed, it is of course, of no use to an open community.

Repraps seem to be a budding industry in itself. No harm in looking at established solutions for inspiration. But is it "cost efficient" (cheap enough), to adopt their solutions as is? If so, which one? I can't think every manufacturer has agreed on a common standard ...

You are echoing a discussion I have had recently with a few other people.

IMHO head development should ideally be entirely be separate from reprap development with, as you suggest, a common multi-pin wiring interface. This means that as far as each tool is concerned the RepRap can be referred to as a host and the head becomes a device. Using this model devices could be controlled using USB 3. This line of reasoning implies that each head having its own USB chip embedded in the tool head which identifies the head and communicates with the host. In this way devices interfaces are standardized and shareable between multiple machines/owners/user groups.

This will also facilitate testing of heads on different Hosts (RepRaps) and consolidate an open and flexible approach to head design in harmony with the RepRap open development philosophy providing both harmony and diversity.

IMHO the starting place would be to agree a minimum standard set of USB host controller capabilities for embedding in the host and a minimum set of signalling capabilities for each device.

I would suggest using 32bit capable USB devices for both Host(RepRap) and Devices(Heads) and a standard physical mount design.

Whilst the USB interface might be standardised at an early stage the mount should be boltable onto the Carriage using a standardised bolt layout so that in that alternative mounting is possible without a complete redesign of the carriage. This would facilitate testing of alternative mounting systems. Certainly seperate power supply socket(s) for the head would seem desirable. I have said sockets on the basis that there should ideally be a standard power head on the basis that the Host should should be capable of supplying an agreed maximum amount of power available for device use but any head requiring more power than the maximum should rely on an independent auxilary power supply. This will make it easier to avoid over-engineering the power supply system for hosts.

I do not have experience in designing USB interfaces but have worked before with people who know how to do this so I am aware of the potentials.

USB is way too complex.
Thinking of a pen-head or a Dremel-holder there's no use in having USB.

I really like the mechanical mounting on the RepMan. Very stable and quick to change the head.
(3 Wing-Bolts in a circle.)
Electricaly they have a standard DIN 25pin socket that carries the signals for 3 too-heads.
Stepper, a resistor to identify the tool-type, heater (or any 12V on/off for that matter), and temperature-sensor (or anything that is input to the ADC).

Let's break such a connection out into e.g. a DIN 9pin socket (the small one used for computer-mice before US
and add a Servo-pin to allow this connetion to be used on the Makerbot-heads.
(They are in need for such a connector and they have a servo on there that is actually used in the pen-head.)

For what it's worth. The subject I started was addressing the grip for the tool head. My goal was to plant the seed for an open standard. A grip that many manufacturers, commercial or otherwise could implement for use interchangeably.

I think the definition of the signals are to be defined a little further ahead. But at least, a few bidirectional signals, some sensing signals and power is needed. And power requires a connector different from that of a computer mouse. If material, granulate plastic string, fluid, cooling is needed in the future, well, leave some room for it.

What is important as I see it, is a trustworthy physical reference point. And the connectors to be located accordingly.

And if the whole thing doesn't cater for easy exchange, then there's little point for it in the first place. I can't see USB or other high level signals belonging to the tool head. That sort is preferably handled by the computer (controller board) located in the bowels of the main machine setup. I have been proved wrong before though ...

Bottom line: What I am talking about is not the head in itself, but the grip to design the tool head for.

So you suggest to include some wires that can carry a larger current then a DIN9 (serial port) connector can handle.
What do you have in mind?
I stated what signals we currently have. What other signal do you suggest to add (as optional ones of cause since current boards do only have the signals I named and not even all of them and the connector must be compatible to current heads and current boards.)

MarcusWolschon Wrote:
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> So you suggest to include some wires that can
> carry a larger current then a DIN9 (serial port)
> connector can handle.

Yes. Melting plastic for extruding is most likely a few Amps. The Molex connector found on a computer PSU handles 15A at 5V easily. Power at a higher voltage is even better. There should be others that are better for snap in and out along with the head.

A DB9 mouse connector are generally rated at 5A max. But it is also difficult to attach large enough wires to the pins. Those connectors are better suited for signals than power.

> What do you have in mind?
> I stated what signals we currently have. What
> other signal do you suggest to add (as optional
> ones of cause since current boards do only have
> the signals I named and not even all of them and
> the connector must be compatible to current heads
> and current boards.)

I can't make up all the requirements of future use. I don't have all the answers. But I doubt that current heads and grips are fully developed at this time.

A constructive discussion is healthy though

Important though is that sensing devices are given good and reliable connection at all times. Even after years of use (and abuse). They give off a very small signal that shouldn't be corrupt by the resistance of a dodgy connector.

Wed Wrote:
> Yes. Melting plastic for extruding is most likely
> a few Amps.

Actually (as I said) the tripple extruder heads of the RepMan ARE
connected that way and work just fine.

> The Molex connector found on a
> computer PSU handles 15A at 5V easily.

That would mean 2 connectors instead of one as you can't run
all the other pins through these.

> A DB9 mouse connector are generally rated at 5A
> max.

That would be 60W at 12V.
the large ones on the Makerbot are e.g. 25W.

> I can't make up all the requirements of future
> use. I don't have all the answers. But I doubt
> that current heads and grips are fully developed
> at this time.

Then don't. Leave some pins as "for future use" or
"printer-dependent" and leave it at that.
There's no problem in having e.g. a separate PC-3.5" drive-style
power-connector if that is ever needed in the future.

> Important though is that sensing devices are given
> good and reliable connection at all times.

Do you mean sensing as in the resistor that identifies
the type of tool-head or as in thermocouple?

> They give off a
> very small signal that shouldn't be corrupt by the
> resistance of a dodgy connector.

That has never been an issue before.
Even with the interference of all the stepper-motors
and the loose pin-head connectors often employed
they always worked fine.
Don't worry about that.

So..... does anyone have an idea for the mechanical
side of a good universal toolhead-mounting?
One that is stable in all 3 axis against backlash,
can support heavy toolheds,
fits into the frame of a RepMan, Mendel, Ting-o-Matic and Mini-Mendel?

VDX Wrote:
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> ... cones with a notch and fixing screws are
> commonly used - all other 'typical' fittings i
> know are special designed and IP'ed for specific
> brands ...

Used for what?
If the toolhead-mount is a cone, where would the tool stick out?

MarcusWolschon Wrote:
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> Used for what?
> If the toolhead-mount is a cone, where would the
> tool stick out?

... cones are common in exchanging heads for milling tools and grippers - sometimes used for other devices too (optics. lasers, dispensers).

The tool 'stick out' on the wide end ... biggest problem is the connection of power, signals and fluids/pneumatics, what's mostly solved with a specific plug interface in the cone-tip, but sometimes with aditional external interfaces too ...

I see.
These large and heavy mounts for industry milling machines with a pneumatic toolhead-grip.
Well...I don't think they are practical for us.
(They are as large as some of the machines here and weight as much as a fully assembled RepMan.)

They are hoewever very good for automatic tool-changers.
Maybe apply 2 cones on the sides of a more conventional mount
to automatically aligh the toolhead and skip any re-calibration after switching a toolhead.

Any idea for a practical automatic fastening between toolhead and toolhead mount
that does not require much space or weight? Bolts are fine for human hands. *thinking*

VDX Wrote:
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> ... but you can apply the cone idea for
> reprap-toolheads too when printing with 'light'
> infill - so the connecting parts will have a solid
> shell and a leightweight body.

That's just the weight.
A cone the size of a toolhead, strong enough to carry a NEMA23 stepper
that is not in the center and a hot-end would probably never fit under the
top bars of a Mendel, have the stepper on the side not fit the hole in
the top of a Thing-o-Matic and simply break off on a RepMan or Darwin
on the first change in direction of the head due to the high center of gravity
on 32-80mm/s print.

What about a circle like the 10056 Extruder Mounting Plate
( [www.bitsfrombytes.com] )
but with 3 small cones in the rim for aligning the tool and some kind of
slot for a servo-operated clamp on both sides to fasten the toolhead in this toolhead-mount.

... there are many different methods around for fixing toolheads - a complete extruder is one of the hardest to solve problems ... but there are pen-holders, dispensers and laser-heads too, what's not so heavy and/or big.

Depending of your goal you'll find different ways, so a 'unified' toolhead-interface for the mendel is a really hard task.

It would be much easier to redesign the machine to get a fixed base for the toolheads and move the table in X, Y and Z (maybe upside-down too) - then the size, weight or interfacing of your toolheads won't be a problem anymore.

VDX Wrote:
-------------------------------------------------------
> ... there are many different methods around for
> fixing toolheads - a complete extruder is one of
> the hardest to solve problems ... but there are
> pen-holders, dispensers and laser-heads too,
> what's not so heavy and/or big.

Indeed.
That's why the mounting must be designed with the
most extreme toolheads in mind.
(large extruders dissipating lots of heat,
heavy backlash of milling heads, ...)

>
> Depending of your goal you'll find different ways,
> so a 'unified' toolhead-interface for the mendel
> is a really hard task.

Yes it is.
It would be a boring task if it would be easy.

> It would be much easier to redesign the machine to
> get a fixed base for the toolheads and move the
> table in X, Y and Z (maybe upside-down too) - then
> the size, weight or interfacing of your toolheads
> won't be a problem anymore.

That would be counterproductive as the task is
not to design a good toolhead-mount for a single new Reprap
but to design a unified toolhead mount for all 3d printers
out there.
That includes a large base of RepMan, Thing-o-Matic,
existing Mendels, Cupcakes, Up! and Darwins.

A new mount that is only used on newer Repraps would
make the problem of not-interchangable toolheads and
duplicated effort worse and not better.

In light of the "common toolhead interface" idea, I propose we go back to RS485 communication between motherboard and toolhead. That way, different heads could each have arduinos embedded, and just tell the motherboard how to control them (i.e., what gcodes get to be forwarded) when they are queried. That way, future heads could be compatible with current firmware, since controlling a head amounts to forwarding appropriate gcodes. Also, the interface would just need four wires (A, B, power, ground) for any toolhead.